Jean-Yves Girard (before he was promoted to !Girard by some fellow ?logicians): I took from him the conviction that there are deep geometrical phenomena at the basis of proof theory, and I found inspiration in linear logic.

Giorgio Levi and Dale Miller: Giorgio made me read and work on Dale's papers, where I could find some excellent design of logical systems.

Christian Retoré: he made me interested in the strange properties of self-duality and non-commutativity and their challenge to proof theory, and he also pointed me to N-free orders, which is where everything started finally to work and make sense.

At TU Dresden I found three bold, extraordinary students: Kai Brünnler, Lutz Straßburger and Alwen Tiu. They risked their future careers to come to work on this project when nobody sane could bet on its success.

Last, but not least, I'd like to acknowledge the Scuola Normale Superiore for the excellent education it tried to give me, at a time when I didn't know that proof theory existed, nor did I know the value of education.